1. Field of the Invention
This invention relates to novel biphenyl compounds which can have a stable thermotropic liquid crystal state and can be utilized as a liquid crystalline material for use in optoelectronics related elements using a liquid crystal and electrochemichromism such as a display for a liquid crystal television receiver, optical printer head, opto-Fourier transform element, light valve and the like as well as liquid crystal compositions containing the above compound and light switching elements using the above compound as a constituent element.
2. Related Art Statement
Liquid crystalline compounds having asymmetric carbon in their molecule can have a chiral smectic C phase in the liquid crystal structure and may exhibit properties as a ferroelectric liquid crystal having a fast response rate, so that they are recently expected as a liquid crystalline material for displaying means requiring a high speed response characteristics. Such a material is required to have properties such a large spontaneous polarization low viscosity the chiral smectic C phase exhibited over a wide temperature range inclusive of room temperature, and the like. However, materials sufficiently satisfying these properties are not yet provided at present.
Particularly, in the case of noticing the fast response characteristics it is preferable to achieve large spontaneous polarization. In this connection, the inventors have previously found that compounds having an asymmetric carbon at an .alpha.-position and ketone group directly bonded to a benzene ring in the molecule are stable against light or the like and wide in the temperature range enantiotropically forming a liquid crystal state. Particularly when optical activity is given to the asymmetric carbon, they become a ferroelectric liquid crystal having a large spontaneous polarization (International Publication No. WO88/07518).
On the other hand, in the case of noticing the low viscosity, the use of biphenyl as a nucelus portion of the liquid crystal is known to be promising. In this connection, there has been proposed a biphenyl compound fepresented by the following formula: ##STR2## (wherein R is a straight or branched alkyl group having a carbon number of 1 to 18) as a compound having an asymmetric carbon at the .alpha.-position and a ketone group directly bonded to biphenyl ring (Japanese Patent laid open No. 60-13729).
However, there is no example for the synthesis of such a biphenyl compound, and also the properties of this biphenyl compound are not clarified at all. Further, the bonding between R and the biphenyl group in the above formula is restricted to only a bond through --O--. However, various changes of the properties can generally be expected by changing a connecting group.